Processing a point cloud

ABSTRACT

At least one embodiment relates to a method for signaling a syntax element representing a Point Local Reconstruction mode, said Point Local Reconstruction mode being representative of at least one parameter defining a mode for reconstructing at least one point of a point cloud frame.

TECHNICAL FIELD

At least one of the present embodiments relates generally to aprocessing of a point cloud.

BACKGROUND

The present section is intended to introduce the reader to variousaspects of art, which may be related to various aspects of at least oneof the present embodiments that is described and/or claimed below. Thisdiscussion is believed to be helpful in providing the reader withbackground information to facilitate a better understanding of thevarious aspects of at least one embodiment.

Point clouds may be used for various purposes such as cultureheritage/buildings in which objects like statues or buildings arescanned in 3D in order to share the spatial configuration of the objectwithout sending or visiting it. Also, it is a way to ensure preservingthe knowledge of the object in case it may be destroyed; for instance, atemple by an earthquake. Such point clouds are typically static, coloredand huge.

Another use case is in topography and cartography in which using 3Drepresentations allows for maps that are not limited to the plane andmay include the relief. Google Maps is now a good example of 3D maps butuses meshes instead of point clouds. Nevertheless, point clouds may be asuitable data format for 3D maps and such point clouds are typicallystatic, colored and huge.

The automotive industry and the autonomous car are also domains in whichpoint clouds may be used. Autonomous cars should be able to “probe”their environment to make good driving decisions based on the reality oftheir immediate neighbors. Typical sensors like LIDARs (Light DetectionAnd Ranging) produce dynamic point clouds that are used by a decisionengine. These point clouds are not intended to be viewed by a humanbeing and they are typically small, not necessarily colored, and dynamicwith a high frequency of capture. These point clouds may have otherattributes like the reflectance provided by the LIDAR as this attributeprovides good information on the material of the sensed object and mayhelp in making decisions.

Virtual Reality and immersive worlds have become hot topics recently andare foreseen by many as the future of 2D flat video. The basic idea isto immerse the viewer in an environment that surrounds the viewer, incontrast to a standard TV in which the viewer can only look at thevirtual world in front of the viewer. There are several gradations inthe immersivity depending on the freedom of the viewer in theenvironment. A point cloud is a good format candidate for distributingVirtual Reality (VR) worlds.

It is important in many applications to be able to distribute dynamicpoint clouds to an end-user (or store them in a server) by consumingonly a reasonable amount of bit-rate (or storage space for storageapplications) while maintaining an acceptable (or preferably very good)quality of experience. Efficient compression of these dynamic pointclouds is a key point in order to make the distribution chain of manyimmersive worlds practical.

At least one embodiment has been devised with the foregoing in mind.

SUMMARY

The following presents a simplified summary of at least one of thepresent embodiments in order to provide a basic understanding of someaspects of the present disclosure. This summary is not an extensiveoverview of an embodiment. It is not intended to identify key orcritical elements of an embodiment. The following summary merelypresents some aspects of at least one of the present embodiments in asimplified form as a prelude to the more detailed description providedelsewhere in the document.

According to a general aspect of at least one embodiment, there isprovided a method comprising signaling in a bitstream a first syntaxelement representing a Point Local Reconstruction mode, said Point LocalReconstruction mode being representative of at least one parameterdefining a mode for reconstructing at least one point of a point cloudframe.

According to an embodiment, said Point Local Reconstruction mode is anindex value of an entry of a look-up-table defining relations betweensaid index value and said at least one parameter.

According to an embodiment, the first syntax element is signaled eitherper block or per patch, a patch being a set of at least one block of 2Dsamples representing an orthogonal projection of at least one 3D sampleof a point cloud frame onto a projection plane.

According to an embodiment, a patch being a set of at least one block ofat least one 2D sample representing an orthogonal projection of at leastone 3D sample of a point cloud frame onto a projection plane, the methodfurther comprises signaling a second syntax element per patch indicatingwhether a single first syntax element is signaled once for all blocks ofa patch or whether a first syntax element is signaled for each block ofa patch.

According to an embodiment, signaling said second syntax element only ifa patch contains more than a given number of blocks.

According to an embodiment, the method further comprises signaling athird syntax element representing a default Point Local Reconstructionmode.

According to an embodiment, signaling said third syntax element perpoint cloud frame and/or per patch, a patch being a set of at least oneblock of 2D samples representing an orthogonal projection of at leastone 3D sample of a point cloud frame onto a projection plane.

According to an embodiment, a patch being a set of at least one block of2D samples representing an orthogonal projection of at least one 3Dsample of a point cloud frame onto a projection plane, the methodfurther comprises signaling a fourth syntax element used to signal agranularity of said first syntax element, per block or per patch, andthe use of said third syntax element per patch.

According to an embodiment, the first syntax element is codeddifferentially from at least one previously signaled first syntaxelement.

One or more of at least one of the present embodiments also provide adevice, a computer program, a signal and a non-transitory computerreadable storage medium.

The specific nature of at least one of the present embodiments as wellas other objects, advantages, features and uses of said at least one ofthe present embodiments will become evident from the followingdescription of examples taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF DRAWINGS

In the drawings, examples of several embodiments are illustrated. Thedrawings show:

FIG. 1 illustrates a schematic block diagram of an example of atwo-layer-based point cloud encoding structure in accordance with atleast one of the present embodiments;

FIG. 2 illustrates a schematic block diagram of an example of atwo-layer-based point cloud decoding structure in accordance with atleast one of the present embodiments;

FIG. 3 illustrates a schematic block diagram of an example of animage-based point cloud encoder in accordance with at least one of thepresent embodiments;

FIG. 3a illustrates an example of a canvas comprising 2 patches andtheir 2D bounding boxes;

FIG. 4 illustrates a schematic block diagram of an example of animage-based point cloud decoder in accordance with at least one of thepresent embodiments;

FIG. 5 illustrates schematically an example of syntax of a bitstreamrepresentative of a base layer BL in accordance with at least one of thepresent embodiments;

FIG. 6 illustrates a schematic block diagram of an example of a systemin which various aspects and embodiments are implemented;

FIG. 7 illustrates a schematic block diagram of an example of a methodfor signaling Point Local Reconstruction mode in accordance with atleast one of the present embodiments;

FIG. 8a-8b illustrate an example of the Look-Up-Table LUT in accordancewith an embodiment of step 710;

FIG. 8c illustrates an example of syntax for signaling the Look-Up-TableLUT in accordance with an embodiment of step 710;

FIG. 8d-8e illustrate an example of embodiments of step 710;

FIG. 9 illustrates an example of an embodiment of the method of FIG. 7;

FIG. 10 illustrates an example of a variant of an embodiment of themethod of FIG. 7;

FIG. 11 illustrates an example of a variant of FIG. 8 c;

FIG. 12a-b illustrate examples of an embodiment of the method of FIG. 7;

FIG. 13 illustrates an example of variant of the method of FIG. 12 b;

FIG. 14 illustrates an example of variant of the method of FIG. 7; and

FIG. 15 illustrates an example of an embodiment of the method of FIG. 7;

DETAILED DESCRIPTION

At least one of the present embodiments is described more fullyhereinafter with reference to the accompanying figures, in whichexamples of at least one of the present embodiments are shown. Anembodiment may, however, be embodied in many alternate forms and shouldnot be construed as limited to the examples set forth herein.Accordingly, it should be understood that there is no intent to limitembodiments to the particular forms disclosed. On the contrary, thedisclosure is intended to cover all modifications, equivalents, andalternatives falling within the spirit and scope of this application.

When a figure is presented as a flow diagram, it should be understoodthat it also provides a block diagram of a corresponding apparatus.Similarly, when a figure is presented as a block diagram, it should beunderstood that it also provides a flow diagram of a correspondingmethod/process.

Similar or same elements of figures are referenced with the samereference numbers.

Some figures represent syntax tables widely used in V-PCC for definingthe structure of a bitstream that conforms with V-PCC. In those syntaxtables, the term ‘ . . . ’ denotes unchanged portions of the syntax withrespect to the original definition given in V-PCC and removed in thefigures to facilitate reading. Bold terms in figures indicate that avalue for this term is obtained by parsing a bitstream. The right columnof the syntax tables indicates the number of bits for encoding a data ofa syntax element. For example, u(4) indicates that 4 bits are used forencoding a data, u(8) indicates 8 bits, ae(v) indicates a contextadaptive arithmetic entropy coded syntax element.

The aspects described and contemplated below may be implemented in manydifferent forms. FIGS. 1-15 below provide some embodiments, but otherembodiments are contemplated, and the discussion of FIGS. 1-15 does notlimit the breadth of the implementations.

At least one of the aspects generally relates to point cloud encodingand decoding, and at least one other aspect generally relates totransmitting a bitstream generated or encoded.

More precisely, various methods and other aspects described herein maybe used to modify modules, for example, modules related to metadataencoding such as those that take places in patch information encoder3700 of FIG. 3 and modules related to metadata decoding such as thosethat take places in the patch information decoder 4400 of FIG. 4, or inthe reconstruction process in the geometry generation module 4500 ofFIG. 4).

Moreover, the present aspects are not limited to MPEG standards such asMPEG-I part 5 that relates to the Point Cloud Compression, and may beapplied, for example, to other standards and recommendations, whetherpre-existing or future-developed, and extensions of any such standardsand recommendations (including MPEG-I part 5). Unless indicatedotherwise, or technically precluded, the aspects described in thisapplication may be used individually or in combination.

In the following, image data refer to data, for example, one or severalarrays of 2D samples in a specific image/video format. A specificimage/video format may specify information pertaining to pixel values ofan image (or a video). A specific image/video format may also specifyinformation which may be used by a display and/or any other apparatus tovisualize and/or decode an image (or video) for example. An imagetypically includes a first component, in the shape of a first 2D arrayof samples, usually representative of luminance (or luma) of the image.An image may also include a second component and a third component, inthe shape of other 2D arrays of samples, usually representative of thechrominance (or chroma) of the image. Some embodiments represent thesame information using a set of 2D arrays of color samples, such as thetraditional tri-chromatic RGB representation.

A pixel value is represented in one or more embodiments by a vector of Cvalues, where C is the number of components. Each value of a vector istypically represented with a number of bits which may define a dynamicrange of the pixel values.

An image block means a set of pixels which belong to an image. The pixelvalues of an image block (or image block data) refer to the values ofthe pixels which belong to this image block. An image block may have anarbitrary shape, although rectangles are common.

A point cloud may be represented by a dataset of 3D samples within a 3Dvolumetric space that have unique coordinates and that may also have oneor more attributes.

A 3D sample of this data set may be defined by its spatial location (X,Y, and Z coordinates in a 3D space) and possibly by one or moreassociated attributes such as a color, represented in the RGB or YUVcolor space for example, a transparency, a reflectance, a two-componentnormal vector or any feature representing a feature of this sample. Forexample, a 3D sample may be defined by 6 components (X, Y, Z, R, G, B)or equivalently (X, Y, Z, y, U, V) where (X,Y,Z) defines the coordinatesof a point in a 3D space and (R,G,B) or (y,U,V) defines a color of this3D sample. The same type of attribute may be present multiple times. Forexample, multiple color attributes may provide color information fromdifferent points of view.

A point cloud may be static or dynamic depending on whether or not thecloud changes with respect to time. A static point cloud or an instanceof a dynamic point cloud is usually denoted as a point cloud frame. Itshould be noticed that in the case of a dynamic point cloud, the numberof points is generally not constant but, on the contrary, generallychanges with time. More generally, a point cloud may be considered asdynamic if anything changes with time, such as, for example, the numberof points, the position of one or more points, or any attribute of anypoint.

As an example, a 2D sample may be defined by 6 components (u, v, Z, R,G, B) or equivalently (u, v, Z, y, U, V). (u,v) defines the coordinatesof a 2D sample in a 2D space of the projection plane. Z is the depthvalue of a projected 3D sample onto this projection plane. (R,G,B) or(y,U,V) defines a color of this 3D sample.

FIG. 1 illustrates a schematic block diagram of an example of atwo-layer-based point cloud encoding structure 1000 in accordance withat least one of the present embodiments.

The two-layer-based point cloud encoding structure 1000 may provide abitstream B representative of an input point cloud frame IPCF. Possibly,said input point cloud frame IPCF represents a frame of a dynamic pointcloud. Then, a frame of said dynamic point cloud may be encoded by thetwo-layer-based point cloud encoding structure 1000 independently fromanother frame.

Basically, the two-layer-based point cloud encoding structure 1000 mayprovide ability to structure the bitstream B as a Base Layer BL and anEnhancement Layer EL. The base layer BL may provide a lossyrepresentation of an input point cloud frame IPCF and the enhancementlayer EL may provide a higher quality (possibly lossless) representationby encoding isolated points not represented by the base layer BL.

The base layer BL may be provided by an image-based encoder 3000 asillustrated in FIG. 3. Said image-based encoder 3000 may providegeometry/texture images representing the geometry/attributes of 3Dsamples of the input point cloud frame IPCF. It may allow isolated 3Dsamples to be discarded. The base layer BL may be decoded by animage-based decoder 4000 as illustrated in FIG. 4 that may provide anintermediate reconstructed point cloud frame IRPCF.

Then, back to the two-layer-based point cloud encoding 1000 in FIG. 1, acomparator COMP may compare the 3D samples of the input point cloudframe IPCF to the 3D samples of the intermediate reconstructed pointcloud frame IRPCF in order to detect/locate missed/isolated 3D samples.Next, an encoder ENC may encode the missed 3D samples and may providethe enhancement layer EL. Finally, the base layer BL and the enhancementlayer EL may be multiplexed together by a multiplexer MUX so as togenerate the bitstream B.

According to an embodiment, the encoder ENC may comprise a detector thatmay detect and associate a 3D reference sample R of the intermediatereconstructed point cloud frame IRPCF to a missed 3D samples M.

For example, a 3D reference sample R associated with a missed 3D sampleM may be its nearest neighbor of M according to a given metric.

According to an embodiment, the encoder ENC may then encode the spatiallocations of the missed 3D samples M and their attributes as differencesdetermined according to spatial locations and attributes of said 3Dreference samples R.

In a variant, those differences may be encoded separately.

For example, fora missed 3D sample M, with spatial coordinates x(M),y(M) and z(M), a x-coordinate position difference Dx(M), a y-coordinateposition difference Dy(M), a z-coordinate position difference Dz(M), aR-attribute component difference Dr(M), a G-attribute componentdifference Dg(M) and the B-attribute component difference Db(M) may becalculated as follows:

Dx(M)=x(M)−x(R),

where x(M) is the x-coordinate of the 3D sample M, respectively R in ageometry image provided by FIG. 3,

Dy(M)=y(M)−y(R)

where y(M) is the y-coordinate of the 3D sample M, respectively R in ageometry image provided by FIG. 3,

Dz(M)=z(M)−z(R)

where z(M) is the z-coordinate of the 3D sample M, respectively R in ageometry image provided by FIG. 3,

Dr(M)=R(M)−R(R).

where R(M), respectively R(R) is the r-color component of a colorattribute of the 3D sample M, respectively R,

Dg(M)=G(M)−G(R).

where G(M), respectively G(R) is the g-color component of a colorattribute of the 3D sample M, respectively R,

Db(M)=B(M)-B(R).

where B(M), respectively B(R) is the b-color component of a colorattribute of the 3D sample M, respectively R.

FIG. 2 illustrates a schematic block diagram of an example of atwo-layer-based point cloud decoding structure 2000 in accordance withat least one of the present embodiments.

The behavior of the two-layer-based point cloud decoding structure 2000depends on its capabilities.

A two-layer-based point cloud decoding structure 2000 with limitedcapabilities may access only the base layer BL from the bitstream B byusing a de-multiplexer DMUX, and then may provide a faithful (but lossy)version IRPCF of the input point cloud frame IPCF by decoding the baselayer BL by a point cloud decoder 4000 as illustrated in FIG. 4.

A two-layer-based point cloud decoding structure 2000 with fullcapabilities may access both the base layer BL and the enhancement layerEL from the bitstream B by using the de-multiplexer DMUX. The pointcloud decoder 4000, as illustrated in FIG. 4, may determine theintermediate reconstructed point cloud frame IRPCF from the base layerBL. The decoder DEC may determine a complementary point cloud frame CPCFfrom the enhancement layer EL. A combiner COM then may combine togetherthe intermediate reconstructed point cloud frame IRPCF and thecomplementary point cloud frame CPCF to therefore provide a higherquality (possibly lossless) representation (reconstruction) CRPCF of theinput point cloud frame IPCF.

FIG. 3 illustrates a schematic block diagram of an example of animage-based point cloud encoder 3000 in accordance with at least one ofthe present embodiments.

The image-based point cloud encoder 3000 leverages existing video codecsto compress the geometry and texture (attribute) information of adynamic point cloud. This is accomplished by essentially converting thepoint cloud data into a set of different video sequences.

In particular embodiments, two videos, one for capturing the geometryinformation of the point cloud data and another for capturing thetexture information, may be generated and compressed using existingvideo codecs. An example of an existing video codec is the HEVC Mainprofile encoder/decoder (ITU-T H.265 Telecommunication standardizationsector of ITU (02/2018), series H: audiovisual and multimedia systems,infrastructure of audiovisual services—coding of moving video, Highefficiency video coding, Recommendation ITU-T H.265).

Additional metadata that are used to interpret the two videos aretypically also generated and compressed separately. Such additionalmetadata includes, for example, an occupancy map OM and/or auxiliarypatch information PI.

The generated video bitstreams and the metadata may be then multiplexedtogether so as to generate a combined bitstream.

It should be noted that the metadata typically represents a small amountof the overall information. The bulk of the information is in the videobitstreams.

An example of such a point cloud coding/decoding process is given by theTest model Category 2 algorithm (also denoted V-PCC) that implements theMPEG draft standard as defined in ISO/IEC JTC1/SC29/VVG11MPEG2019/w18180 (January 2019, Marrakesh).

In step 3100, a module PGM may generate at least one patch bydecomposing 3D samples of a data set representative of the input pointcloud frame IPCF to 2D samples on a projection plane using a strategythat provides best compression.

A patch may be defined as a set of 2D samples.

For example, in V-PCC, a normal at every 3D sample is first estimated asdescribed, for example, in Hoppe et al. (Hugues Hoppe, Tony DeRose, TomDuchamp, John McDonald, Werner Stuetzle. Surface reconstruction fromunorganized points. ACM SIGGRAPH 1992 Proceedings, 71-78). Next, aninitial clustering of the input point cloud frame IPCF is obtained byassociating each 3D sample with one of the six oriented planes of a 3Dbounding box encompassing the 3D samples of the input point cloud frameIPCF. More precisely, each 3D sample is clustered and associated with anoriented plane that has the closest normal (that is maximizes the dotproduct of the point normal and the plane normal). Then the 3D samplesare projected to their associated planes. A set of 3D samples that formsa connected area in their plane is referred as a connected component. Aconnected component is a set of at least one 3D sample having similarnormal and a same associated oriented plane. The initial clustering isthen refined by iteratively updating the cluster associated with each 3Dsample based on its normal and the clusters of its nearest neighboringsamples. The final step consists of generating one patch from eachconnected component, that is done by projecting the 3D samples of eachconnected component onto the oriented plane associated with saidconnected component. A patch is associated with auxiliary patchinformation PI that represents auxiliary patch information defined foreach patch to interpret the projected 2D samples that correspond to thegeometry and/or attribute information.

In V-PCC, for example, the auxiliary patch information PI includes 1)information indicating one of the six oriented planes of a 3D boundingbox encompassing the 3D samples of a connected component; 2) informationrelative to the plane normal; 3) information determining the 3D locationof a connected component relative to a patch represented in terms ofdepth, tangential shift and bi-tangential shift; and 4) information suchas coordinates (u0, v0, u1, v1) in a projection plane defining a 2Dbounding box encompassing a patch.

In step 3200, a patch packing module PPM may map (place) at least onegenerated patch onto a 2D grid (also called canvas) without anyoverlapping in a manner that typically minimizes the unused space, andmay guarantee that every T×T (for example, 16×16) block of the 2D gridis associated with a unique patch. A given minimum block size T×T of the2D grid may specify the minimum distance between distinct patches asplaced on this 2D grid. The 2D grid resolution may depend on the inputpoint cloud size and its width W and height H and the block size T maybe transmitted as metadata to the decoder.

The auxiliary patch information PI may further include informationrelative to an association between a block of the 2D grid and a patch.

In V-PCC, the auxiliary information PI may include a block to patchindex information (BlockToPatch) that determines an association betweena block of the 2D grid and a patch index.

FIG. 3a illustrates an example of a canvas C comprising 2 patches P1 andP2 and their associated 2D bounding boxes B1 and B2. Note that twobounding boxes may overlap in the canvas C as illustrated on FIG. 3a .The 2D grid (the splitting of the canvas) is only represented inside thebounding box but the splitting of the canvas also occurs outside thosebounding boxes. A bounding box associated with a patch can be split intoT×T blocks, typically T=16.

T×T blocks containing 2D samples belonging to a patch may be consideredas occupied blocks in the corresponding occupancy map OM. A block of theoccupancy map OM may then indicate whether a block is occupied, that iscontains 2D samples that belong to a patch.

In FIG. 3a , an occupied block is represented by a white block and lightgrey blocks represent unoccupied blocks. The image generation processes(steps 3300 and 3400) exploit the mapping of the at least one generatedpatch onto the 2D grid computed during step 3200, to store the geometryand texture of the input point cloud frame IPCF as images.

In step 3300, a geometry image generator GIG may generate at least onegeometry image GI from the input point cloud frame IPCF, the occupancymap OM and the auxiliary patch information PI. The geometry imagegenerator GIG may exploit the occupancy map information in order todetect (locate) the occupied blocks and thus the non-empty pixels in thegeometry image GI.

A geometry image GI may represent the geometry of the input point cloudframe IPCF and may be a monochromatic image of W×H pixels represented,for example, in YUV420-8 bit format.

In order to better handle the case of multiple 3D samples beingprojected (mapped) to a same 2D sample of the projection plane (along asame projection direction (line)), multiple images, referred to aslayers, may be generated. Thus, different depth values D1, . . . , Dnmay be associated with a 2D sample of a patch and multiple geometryimages may then be generated.

In V-PCC, 2D samples of a patch are projected onto two layers. A firstlayer, also called the near layer, may store, for example, the depthvalues D0 associated with the 2D samples with smaller depths. A secondlayer, referred to as the far layer, may store, for example, the depthvalues D1 associated with the 2D samples with larger depths.Alternatively, the second layer may store difference values betweendepth values D1 and D0. For example, the information stored by thesecond depth image may be within an interval [0, Δ] corresponding todepth values in the range [D0, D0+Δ], where A is a user-definedparameter that describes the surface thickness.

By this way, the second layer may contain significant contour-like highfrequency features. Thus, it clearly appears that the second depth imagemay be difficult to code by using a legacy video coder and, therefore,the depth values may be poorly reconstructed from said decoded seconddepth image, which results on a poor quality of the geometry of thereconstructed point cloud frame.

According to an embodiment, the geometry image generating module GIG maycode (derive) depth values associated with 2D samples of the first andsecond layers by using the auxiliary patch information PI.

In V-PCC, the location of a 3D sample in a patch with a correspondingconnected component may be expressed in terms of depth δ(u, v),tangential shift s(u, v) and bi-tangential shift r(u, v) as follows:

δ(u,v)=δ0+g(u,v)

s(u,v)=s0−u0+u

r(u,v)=r0−v0+v

where g(u, v) is the luma component of the geometry image, (u,v) is apixel associated with the 3D sample on a projection plane, (δ0, s0, r0)is the 3D location of the corresponding patch of a connected componentto which the 3D sample belongs and (u0, v0, u1, v1) are the coordinatesin said projection plane defining a 2D bounding box encompassing theprojection of the patch associated with said connected component.

Thus, a geometry image generating module GIG may code (derive) depthvalues associated with 2D samples of a layer (first or second or both)as a luma component g(u,v) given by: g(u,v)=δ(u, v)−δ0. It is noted thatthis relationship may be employed to reconstruct 3D sample locations(δ0, s0, r0) from a reconstructed geometry image g(u, v) with theaccompanying auxiliary patch information PI.

According to an embodiment, a projection mode may be used to indicate ifa first geometry image GI0 may store the depth values of the 2D samplesof either the first or second layer and a second geometry image GI1 maystore the depth values associated with the 2D samples of either thesecond or first layer.

For example, when a projection mode equals 0, then the first geometryimage GI0 may store the depth values of 2D samples of the first layerand the second geometry image GI1 may store the depth values associatedwith 2D samples of the second layer. Reciprocally, when a projectionmode equals 1, then the first geometry image GI0 may store the depthvalues of 2D samples of the second layer and the second geometry imageGI1 may store the depth values associated with 2D samples of the firstlayer.

According to an embodiment, a frame projection mode may be used toindicate if a fixed projection mode is used for all the patches or if avariable projection mode is used in which each patch may use a differentprojection mode.

The projection mode and/or the frame projection mode may be transmittedas metadata.

A frame projection mode decision algorithm may be provided, for example,in section 2.2.1.3.1 of V-PCC.

According to an embodiment, when the frame projection indicates that avariable projection mode may be used, a patch projection mode may beused to indicate the appropriate mode to use to (de-)project a patch.

A patch projection mode may be transmitted as metadata and may be,possibly, an information included in the auxiliary patch information PI.

A patch projection mode decision algorithm is provided, for example insection 2.2.1.3.2 of V-PCC.

According to an embodiment of step 3300, the pixel value in a firstgeometry image, for example GI0, corresponding to a 2D sample (u,v) of apatch may represent the depth values associated with at least onein-between 3D samples defined along a projection line corresponding tosaid 2D sample (u,v). Said in-between 3D samples reside along aprojection line and share the same coordinates of the 2D sample (u,v)whose depth value D1 is coded in a second geometry image, for exampleGI1. Further, the said in-between 3D samples may have depth valuesbetween the depth value D0 and a depth value D1. A designated bit may beassociated with each said in-between 3D samples which is set to 1 if thein-between 3D sample exists and 0 otherwise.

Then, all said designated bits along said projection line may beconcatenated to form a codeword, called as Enhanced-Delta-Depth (EDD)code hereafter. Finally, all the EDD codes may be packed in an image,for example in the first geometry image GI1 or the occupancy map OM.

In step 3400, a texture image generator TIG may generate at least onetexture image TI from the input point cloud frame IPCF, the occupancymap OM, the auxiliary patch information PI and a geometry of areconstructed point cloud frame derived from at least one decodedgeometry image DGI, output of a video decoder VDEC (step 4200 in FIG.4).

A texture image TI may represent the texture of the input point cloudframe IPCF and may be an image of W×H pixels represented, for example,in YUV420-8 bit format.

The texture image generator TG may exploit the occupancy map informationin order to detect (locate) the occupied blocks and thus the non-emptypixels in the texture image.

The texture image generator TIG may be adapted to generate and associatea texture image TI with each geometry image/layer DGI.

According to an embodiment, the texture image generator TIG may code(store) the texture (attribute) values T0 associated with 2D samples ofthe first layer as pixel values of a first texture image TI0 and thetexture values T1 associated with the 2D samples of the second layer aspixel values of a second texture image TI1.

Alternatively, the texture image generating module TIG may code (store)the texture values T1 associated with 2D samples of the second layer aspixel values of the first texture image TI0 and the texture values D0associated with the 2D samples of the first layer as pixel values of thesecond geometry image GI1.

For example, colors of 3D samples may be obtained as described insection 2.2.3, 2.2.4, 2.2.5, 2.2.8 or 2.5 of V-PCC.

According to an embodiment, a padding process may be applied on thegeometry and/or texture image. The padding process may be used to fillempty space between patches to generate a piecewise smooth image suitedfor video compression.

An image padding example is provided in sections 2.2.6 and 2.2.7 ofV-PCC.

In step 3500, a video encoder VENC may encode the generatedimages/layers TI and GI.

In step 3600, an encoder OMENC may encode the occupancy map as an imageas detailed, for example, in section 2.2.2 of V-PCC. Lossy or losslessencoding may be used.

According to an embodiment, the video encoder ENC and/or OMENC may be aHEVC-based encoder.

In step 3700, an encoder PIENC may encode the auxiliary patchinformation PI and possibly additional metadata such as the block sizeT, the width W and height H of the geometry/texture images.

According to an embodiment, the auxiliary patch information may bedifferentially encoded (as defined, for example in section 2.4.1 ofV-PCC).

In step 3800, a multiplexer may be applied to the generated outputs ofsteps 3500, 3600 and 3700, and as a result these outputs may bemultiplexed together so as to generate a bitstream representative of thebase layer BL. It should be noted that the metadata informationrepresents a small fraction of the overall bitstream. The bulk of theinformation is compressed using the video codecs.

FIG. 4 illustrates a schematic block diagram of an example of animage-based point cloud decoder 4000 in accordance with at least one ofthe present embodiments.

In step 4100, a de-multiplexer DMUX may applied to demutiplex theencoded information of the bitstream representative of the base layerBL.

In step 4200, a video decoder VDEC may decode encoded information toderive at least one decoded geometry image DGI and at least one decodedtexture image DTI.

In step 4300, a decoder OMDEC may decode encoded information to derive adecoded occupancy map DOM.

According to an embodiment, the video decoder VDEC and/or OMDEC may be aHEVC-based decoder.

In step 4400, a decoder PIDEC may decode encoded information to deriveauxiliary patch information DPI.

Possibly, metadata may also be derived from the bitstream BL.

In step 4500, a geometry generating module GGM may derive the geometryRG of a reconstructed point cloud frame IRPCF from the at least onedecoded geometry image DGI, the decoded occupancy map DOM, the decodedauxiliary patch information DPI and possible additional metadata.

The geometry generating module GGM may exploit the decoded occupancy mapinformation DOM in order to locate the non-empty pixels in the at leastone decoded geometry image DGI. The 3D coordinates of reconstructed 3Dsamples associated with non-empty pixels may then be derived from thecoordinates of said non-empty pixels and the values of saidreconstructed 2D samples.

According to an embodiment, the geometry generating module GGM mayderive the 3D coordinates of reconstructed 3D samples from coordinatesof non-empty pixels.

According to an embodiment, the geometry generating module GGM mayderive the 3D coordinates of reconstructed 3D samples from coordinatesof non-empty pixels, values of said non-empty pixels of one of the atleast one decoded geometry image DGI, the decoded auxiliary patchinformation, and possibly, from additional metadata.

The use of non-empty pixels is based on 2D pixel relationship with 3Dsamples. For example, with the said projection in V-PCC, the 3Dcoordinates of reconstructed 3D samples may be expressed in terms ofdepth δ(u, v), tangential shift s(u, v) and bi-tangential shift r(u, v)as follows:

δ(u,v)=δ0+g(u,v)

s(u,v)=s0−u0+u

r(u,v)=r0−v0+v

where g(u, v) is the luma component of a decoded geometry image DGI,(u,v) is a pixel associated with a reconstructed 3D sample, (δ0, s0, r0)is the 3D location of a connected component to which the reconstructed3D sample belongs and (u0, v0, u1, v1) are the coordinates in aprojection plane defining a 2D bounding box encompassing the projectionof a patch associate with said connected component.

In step 4600, a texture generating module TGM may derive the texture ofthe reconstructed point cloud frame IRPCF from the geometry RG and theat least one decoded texture image DTI.

FIG. 5 illustrates schematically an example syntax of a bitstreamrepresentative of a base layer BL in accordance with at least one of thepresent embodiments.

The bitstream comprises a Bitstream Header SH and at least one Group OfFrame Stream GOFS.

A group of frame stream GOFS comprises a header HS, at least one syntaxelement OMS representative of an occupancy map OM, at least one syntaxelement GVS representative of at least one geometry image (or video), atleast one syntax element TVS representative of at least one textureimage (or video) and at least one syntax element PIS representative ofauxiliary patch information and other additional metadata.

In a variant, a group of frame stream GOFS comprises at least one framestream.

FIG. 6 shows a schematic block diagram illustrating an example of asystem in which various aspects and embodiments are implemented.

System 6000 may be embodied as one or more devices including the variouscomponents described below and is configured to perform one or more ofthe aspects described in this document. Examples of equipment that mayform all or part of the system 6000 include personal computers, laptops,smartphones, tablet computers, digital multimedia set top boxes, digitaltelevision receivers, personal video recording systems, connected homeappliances, connected vehicles and their associated processing systems,head mounted display devices (HMD, see-through glasses), projectors(beamers), “caves” (system including multiple displays), servers, videoencoders, video decoders, post-processors processing output from a videodecoder, pre-processors providing input to a video encoder, web servers,set-top boxes, and any other device for processing a point cloud, avideo or an image or other communication devices. Elements of system6000, singly or in combination, may be embodied in a single integratedcircuit, multiple ICs, and/or discrete components. For example, in atleast one embodiment, the processing and encoder/decoder elements ofsystem 6000 may be distributed across multiple ICs and/or discretecomponents. In various embodiments, the system 6000 may becommunicatively coupled to other similar systems, or to other electronicdevices, via, for example, a communications bus or through dedicatedinput and/or output ports. In various embodiments, the system 6000 maybe configured to implement one or more of the aspects described in thisdocument.

The system 6000 may include at least one processor 6010 configured toexecute instructions loaded therein for implementing, for example, thevarious aspects described in this document. Processor 6010 may includeembedded memory, input output interface, and various other circuitriesas known in the art. The system 6000 may include at least one memory6020 (for example a volatile memory device and/or a non-volatile memorydevice). System 6000 may include a storage device 6040, which mayinclude non-volatile memory and/or volatile memory, including, but notlimited to, Electrically Erasable Programmable Read-Only Memory(EEPROM), Read-Only Memory (ROM), Programmable Read-Only Memory (PROM),Random Access Memory (RAM), Dynamic Random Access Memory (DRAM), StaticRandom Access Memory (SRAM), flash, magnetic disk drive, and/or opticaldisk drive. The storage device 6040 may include an internal storagedevice, an attached storage device, and/or a network accessible storagedevice, as non-limiting examples.

The system 6000 may include an encoder/decoder module 6030 configured,for example, to process data to provide encoded data or decoded data,and the encoder/decoder module 6030 may include its own processor andmemory. The encoder/decoder module 6030 may represent module(s) that maybe included in a device to perform the encoding and/or decodingfunctions. As is known, a device may include one or both of the encodingand decoding modules. Additionally, encoder/decoder module 6030 may beimplemented as a separate element of system 6000 or may be incorporatedwithin processor 6010 as a combination of hardware and software as knownto those skilled in the art.

Program code to be loaded onto processor 6010 or encoder/decoder 6030 toperform the various aspects described in this document may be stored instorage device 6040 and subsequently loaded onto memory 6020 forexecution by processor 6010. In accordance with various embodiments, oneor more of processor 6010, memory 6020, storage device 6040, andencoder/decoder module 6030 may store one or more of various itemsduring the performance of the processes described in this document. Suchstored items may include, but are not limited to, a point cloud frame,encoded/decoded geometry/texture videos/images or portions of theencoded/decoded geometry/texture video/images, a bitstream, matrices,variables, and intermediate or final results from the processing ofequations, formulas, operations, and operational logic.

In several embodiments, memory inside of the processor 6010 and/or theencoder/decoder module 6030 may be used to store instructions and toprovide working memory for processing that may be performed duringencoding or decoding.

In other embodiments, however, a memory external to the processingdevice (for example, the processing device may be either the processor6010 or the encoder/decoder module 6030) may be used for one or more ofthese functions. The external memory may be the memory 6020 and/or thestorage device 6040, for example, a dynamic volatile memory and/or anon-volatile flash memory. In several embodiments, an externalnon-volatile flash memory may be used to store the operating system of atelevision. In at least one embodiment, a fast external dynamic volatilememory such as a RAM may be used as working memory for video coding anddecoding operations, such as for MPEG-2 part 2 (also known as ITU-TRecommendation H.262 and ISO/IEC 13818-2, also known as MPEG-2 Video),HEVC (High Efficiency Video coding), or WC (Versatile Video Coding).

The input to the elements of system 6000 may be provided through variousinput devices as indicated in block 6130. Such input devices include,but are not limited to, (i) an RF portion that may receive an RF signaltransmitted, for example, over the air by a broadcaster, (ii) aComposite input terminal, (iii) a USB input terminal, and/or (iv) anHDMI input terminal.

In various embodiments, the input devices of block 6130 may haveassociated respective input processing elements as known in the art. Forexample, the RF portion may be associated with elements necessary for(i) selecting a desired frequency (also referred to as selecting asignal, or band-limiting a signal to a band of frequencies), (ii)down-converting the selected signal, (iii) band-limiting again to anarrower band of frequencies to select (for example) a signal frequencyband which may be referred to as a channel in certain embodiments, (iv)demodulating the down-converted and band-limited signal, (v) performingerror correction, and (vi) demultiplexing to select the desired streamof data packets. The RF portion of various embodiments may include oneor more elements to perform these functions, for example, frequencyselectors, signal selectors, band-limiters, channel selectors, filters,downconverters, demodulators, error correctors, and de-multiplexers. TheRF portion may include a tuner that performs various of these functions,including, for example, down-converting the received signal to a lowerfrequency (for example, an intermediate frequency or a near-basebandfrequency) or to baseband.

In one set-top box embodiment, the RF portion and its associated inputprocessing element may receive an RF signal transmitted over a wired(for example, cable) medium. Then, the RF portion may perform frequencyselection by filtering, down-converting, and filtering again to adesired frequency band.

Various embodiments rearrange the order of the above-described (andother) elements, remove some of these elements, and/or add otherelements performing similar or different functions.

Adding elements may include inserting elements in between existingelements, such as, for example, inserting amplifiers and ananalog-to-digital converter. In various embodiments, the RF portion mayinclude an antenna.

Additionally, the USB and/or HDMI terminals may include respectiveinterface processors for connecting system 6000 to other electronicdevices across USB and/or HDMI connections. It is to be understood thatvarious aspects of input processing, for example, Reed-Solomon errorcorrection, may be implemented, for example, within a separate inputprocessing IC or within processor 6010 as necessary. Similarly, aspectsof USB or HDMI interface processing may be implemented within separateinterface ICs or within processor 6010 as necessary. The demodulated,error corrected, and demultiplexed stream may be provided to variousprocessing elements, including, for example, processor 6010, andencoder/decoder 6030 operating in combination with the memory andstorage elements to process the data stream as necessary forpresentation on an output device.

Various elements of system 6000 may be provided within an integratedhousing. Within the integrated housing, the various elements may beinterconnected and transmit data therebetween using suitable connectionarrangement 6140, for example, an internal bus as known in the art,including the I2C bus, wiring, and printed circuit boards.

The system 6000 may include communication interface 6050 that enablescommunication with other devices via communication channel 6060. Thecommunication interface 6050 may include, but is not limited to, atransceiver configured to transmit and to receive data overcommunication channel 6060. The communication interface 6050 mayinclude, but is not limited to, a modem or network card and thecommunication channel 6060 may be implemented, for example, within awired and/or a wireless medium.

Data may be streamed to the system 6000, in various embodiments, using aWi-Fi network such as IEEE 802.11. The Wi-Fi signal of these embodimentsmay be received over the communications channel 6060 and thecommunications interface 6050 which are adapted for Wi-Ficommunications. The communications channel 6060 of these embodiments maybe typically connected to an access point or router that provides accessto outside networks including the Internet for allowing streamingapplications and other over-the-top communications.

Other embodiments may provide streamed data to the system 6000 using aset-top box that delivers the data over the HDMI connection of the inputblock 6130.

Still other embodiments may provide streamed data to the system 6000using the RF connection of the input block 6130.

It is to be appreciated that signaling may be accomplished in a varietyof ways. For example, one or more syntax elements, flags, and so forthmay be used to signal information to a corresponding decoder in variousembodiments.

The system 6000 may provide an output signal to various output devices,including a display 6100, speakers 6110, and other peripheral devices6120. The other peripheral devices 6120 may include, in various examplesof embodiments, one or more of a stand-alone DVR, a disk player, astereo system, a lighting system, and other devices that provide afunction based on the output of the system 3000.

In various embodiments, control signals may be communicated between thesystem 6000 and the display 6100, speakers 6110, or other peripheraldevices 6120 using signaling such as AV.Link (Audio/Video Link), CEC(Consumer Electronics Control), or other communications protocols thatenable device-to-device control with or without user intervention.

The output devices may be communicatively coupled to system 6000 viadedicated connections through respective interfaces 6070, 6080, and6090.

Alternatively, the output devices may be connected to system 6000 usingthe communications channel 6060 via the communications interface 6050.The display 6100 and speakers 6110 may be integrated in a single unitwith the other components of system 6000 in an electronic device suchas, for example, a television.

In various embodiments, the display interface 6070 may include a displaydriver, such as, for example, a timing controller (T Con) chip.

The display 6100 and speaker 6110 may alternatively be separate from oneor more of the other components, for example, if the RF portion of input6130 is part of a separate set-top box. In various embodiments in whichthe display 6100 and speakers 6110 may be external components, theoutput signal may be provided via dedicated output connections,including, for example, HDMI ports, USB ports, or COMP outputs.

PLR stands for Point Local Reconstruction. PLR is a reconstructionmethod that may be used to generate additional 3D samples to a pointcloud frame. PLR is typically applied immediately after a 2D to 3Dprojection, before any other processing like, for example, geometry ortexture smoothing.

PLR takes a layer of 3D samples as input and applies a set of filtersdriven by PLR metadata to generate additional 3D samples, with theirgeometry and texture.

PLR may be local because PLR metadata may change per T×T block of thecanvas and the set of filters may use a small neighborhood to generatethe additional 3D samples. Note that same PLR metadata must be used inthe encoder and the decoder.

In typical conditions, using a single layer of depth and texture imageswith PLR provides better BD-rate performance than two-layers of depthand texture images. The coding of PLR metadata takes fewer bits thanconventional coding of 3D samples thru projection onto depth and textureimages, therefore the overall bitrate is reduced. At the same time, theadditional 3D samples compensate for the loss of quality caused by usingfewer layers.

V-PCC includes an implementation of a PLR, where PLR is determined onencoder side by RDO (Rate-Distortion Optimization). Said implementationof PLR defines multiple modes, denoted PLRM (Point Local ReconstructionMode), for reconstructing (generating) at least one 3D sample of a pointcloud frame. Each PLRM is determined by specific values of PLRM metadatathat defined how the filters are used.

For example, in section “9.4.4” of V-PCC, multiple PLRM are determinedby four parameters described in section “7.4.35 Point localreconstruction semantics” of V-PCC. Said four parameters are transmittedas PLRM metadata in the bitstream:

-   -   point_local_reconstruction_mode_interpolate_flag:    -   This parameter equals 1 to indicate that point interpolation is        used during the reconstruction method; This parameter equals 0        to indicate that no point interpolation is used during the        reconstruction method;    -   point_local_reconstruction_mode_filling_flag    -   This parameter equals 1 to indicate that the filling mode is        used during the reconstruction method; This parameter equals 0        to indicate that the filling mode is not used during the        reconstruction process.    -   pointlocal_reconstruction_mode_minimum_depth_minus1:    -   This parameter specifies the minimum depth value minus 1 to be        used during the reconstruction method.    -   pointlocal_reconstruction_mode_neighbour_minus1:    -   This parameter specifies the size minus 1 of the 2D        neighbourhood to be used in the reconstruction method.

A syntax for coding PLR is detailed in section “7.3.35 Point localreconstruction syntax” of V-PCC. This syntax describes the PLRM metadatasent by T×T block (the occupancy packing block size) through the“blockToPatch” information. The blockToPatch structure indicates foreach block of T×T pixels the patch it belongs to. The size of 16×16pixels for the block-to-patch block is the typical value used in theV-FCC test model software. The specification (and at least one of thepresent embodiments) may support other block sizes for block-to-patchindex and PLRM metadata.

PLR metadata may be retrieved from a bitstream as follows: A loopiterates over all the T×T blocks of the canvas in a scanning order, forexample a raster scanning order. For each block of the canvas, if theoccupancy map OM indicates that said block is unoccupied, then proceededto the next block. Otherwise, that is the block is occupied, the blockto patch information BlockToPatch is retrieved from a bitstream in orderto obtain the patch ID of said block, and the PLR parameters for saidoccupied block is retrieved from the bitstream.

In the current implementations of point cloud coding (V-PCC), decodingthe PLR metadata from a bitstream requires intensive computing resources(CPU, GPU, memory) because four parameters have to be decoded for eachT×T block.

According to a general aspect of at least one embodiment, there isprovided a method for signaling a syntax element representing a PointLocal Reconstruction mode, said Point Local Reconstruction mode beingrepresentative of at least one parameter defining a mode forreconstructing at least one point of a point cloud frame.

Signaling a syntax element rather than four parameters per block mayreduce the computing resources at the decoding side as defined in V-PCCbecause said syntax element may be signaled per patch or per point cloudframe. This also provides flexibility for signaling PLRM metadata.

FIG. 7 illustrates a schematic block diagram of an example of a methodfor signaling Point Local Reconstruction modes in accordance with atleast one of the present embodiments.

In step 710, a module may add, in a bitstream, at least one syntaxelement SE1 representing a Point Local Reconstruction mode, denotedPLRM. Said PLRM represents at least one parameter defining a mode forreconstructing at least one 3D sample of a point cloud frame.

In step 740, the bitstream is transmitted.

In step 770, a module may retrieve (read) from a bitstream (receivedbitstream) at least one first syntax element SE1 at least one PLRM to beused for reconstructing at least one 3D sample of the point cloud.

At least one parameter is retrieved from said at least one syntaxelement SE1 and at least one 3D sample of the point cloud is thenreconstructed using said at least one PLRM.

According to an embodiment of step 710, a PLRM may be an index value ofan entry of a look-up-table LUT. Each entry of said LUT defines arelation between an index value and at least one parameter defining aspecific mode for reconstructing at least one point of said point cloudframe.

FIG. 8a-8b illustrate an example of the Look-Up-Table LUT in accordancewith an embodiment of step 710.

The left column indicates different values of PLRM, each PLRM defining acombination of 4 parameters I, F, D1min and N that determines areconstruction method using a combination of the following tools asexplained before:

-   pointlocal_reconstruction_mode_interpolate_flag,-   pointlocal_reconstruction_mode;-   pointlocal_reconstruction_mode_minimum_depth_minus1 and-   pointlocal_reconstruction_mode_neighbour_minus1

The PLRM 0 of FIG. 8a indicates that “no PLRM metadata” is used, i.e. noPLR metadata is transmitted.

Such a PLRM mode is removed from the look-up-table LUT of FIG. 8b . Inthat case the “no PLRM metadata” mode is signaled elsewhere.

FIG. 8c illustrates an example of syntax for signaling the Look-Up-TableLUT in accordance with an embodiment of step 710.

According to an embodiment of step 710, the first syntax element SE1 maybe signaled per block as illustrated in FIG. 8d in whichpointlocal_reconstruction_mode[p][i] refers to a syntax element SE1associated with a block i of a patch p.

According to an embodiment of step 710, the first syntax element SE1 maybe signaled per patch as illustrated in FIG. 8e in whichpointlocal_reconstruction_mode[p] refers to a first syntax element SE1associated with a patch p.

In step 720 (optional), a module may add in the bitstream a secondsyntax element SE2 per patch indicating whether a single first syntaxelement SE1 is signaled once for all blocks of a patch or whether afirst syntax element SE1 is signaled for each block of a patch.

When a second syntax element SE2 indicates a single first syntax elementis once signaled for all blocks of a patch, said single first syntaxelement is used for all blocks of said patch and is thus signaled at thepatch level.

As illustrated in FIG. 9, pointlocal_reconstruction_patchlevel[p] refersto a second syntax element SE2:pointlocal_reconstruction_patchlevel[p]=0 means a first syntax elementpointlocal_reconstruction_mode[p][i] is signaled for each block of apatch and pointlocal_reconstruction_patchlevel[p]=1 means a first syntaxelement pointlocal_reconstruction_mode[p] is signaled per once for allblocks of a patch p.

According to a variant of step 720, a second syntax element SE2 may besignaled only if a patch contains more than a given number of blocks.

As illustrated in FIG. 10, BlockCountThreshold refers to a given numberof blocks. When the number of blocks in a patch is greater than orequals to BlockCountThreshold, the second syntax elementpoint_local_reconstruction_patch_level[p] is set to 0 (a first syntaxelement pointlocal_reconstruction_mode[p] is signaled per block).Otherwise it is set to 1 (a first syntax elementpointlocal_reconstruction_mode[p] is signaled per patch).

In step 730 (optional), a module may add in a bitstream at least onethird syntax element SE3 representing a default Point LocalReconstruction mode, also denoted a preferred Point Local Reconstructionmode.

As illustrated in FIG. 12a-b , point_local_reconstruction_preferred_moderefers to a third syntax element SE3.

FIG. 11 illustrates an example for signaling the Look-Up-Table LUT(first syntax element SE1) in accordance with an embodiment of step 710and point_local_reconstruction_preferred_mode.

According to an embodiment of step 730, a third syntax element SE3 maybe signaled per point cloud frame and/or per patch.

As illustrated in FIG. 13,point_local_reconstruction_preferred_mode_patch[p] refers to a thirdsyntax element SE3 signaled per patch, andpoint_local_reconstruction_preferred_mode refers to a third syntaxelement SE3 signaled per point cloud frame.

As illustrated in FIG. 15, point_local_reconstruction_preferred_moderefers to a third syntax element SE3 signaled per point cloud frame.

According to an embodiment of step 740, a module may add in a bitstreama fourth syntax element SE4 used to signal a granularity of the firstsignal element SE1 (PLRM per block or per patch) and the use of a thirdsyntax element SE3 (a default Point Local Reconstruction mode signaledper patch).

As illustrated in FIG. 12a-b , point_local_reconstruction_patch_level[p] refers to a fourth syntax element. Whenpoint_local_reconstruction_patch_level [p]=0, then a first syntaxelement SE1 (point_local_reconstruction_mode[p][i]) is signaled perblock i; when point_local_reconstruction_patch_level [p]=1, then a firstsyntax element SE1 (point_local_reconstruction_mode[p]) is signaled perpatch p and, otherwise a third syntax element SE3(point_local_reconstruction_preferred_mode) is signaled for all blocksof a patch p.

In FIG. 12a , point_local_reconstruction_preferred_mode is signaled perpoint cloud frame.

In FIG. 12b , point_local_reconstruction_preferred_mode_patch[p] issignaled per patch.

FIG. 13 illustrates an example of variant of FIG. 12b when a secondsyntax element SE2 is signaled only if a patch contains more than agiven number of blocks BlockCountThreshold.

FIG. 14 illustrates an example of said variant when a first syntaxelement point_local_reconstruction_mode[p][i] is signaled per block(FIG. 8d ): point_local_reconstruction_mode_delta replacespoint_local_reconstruction_mode[p][i].

Said variant may also applied to other examples for signaling a firstsyntax element SE1 as illustrated, for example, in FIG. 8e , 9, 10, 12a-b, 12 a and 13.

Said variant may also applied for differentially encoding a secondsyntax element SE2 as illustrated, for example, in FIG. 9, 10, 12 a-band 13.

In FIG. 1-15, various methods are described herein, and each of themethods includes one or more steps or actions for achieving thedescribed method. Unless a specific order of steps or actions isrequired for proper operation of the method, the order and/or use ofspecific steps and/or actions may be modified or combined.

Some examples are described with regard to block diagrams andoperational flowcharts. Each block represents a circuit element, module,or portion of code which includes one or more executable instructionsfor implementing the specified logical function(s). It should also benoted that in other implementations, the function(s) noted in the blocksmay occur out of the indicated order. For example, two blocks shown insuccession may, in fact, be executed substantially concurrently or theblocks may sometimes be executed in the reverse order, depending on thefunctionality involved.

The implementations and aspects described herein may be implemented in,for example, a method or a process, an apparatus, a computer program, adata stream, a bitstream, or a signal. Even if only discussed in thecontext of a single form of implementation (for example, discussed onlyas a method), the implementation of features discussed may also beimplemented in other forms (for example, an apparatus or computerprogram).

The methods may be implemented in, for example, a processor, whichrefers to processing devices in general, including, for example, acomputer, a microprocessor, an integrated circuit, or a programmablelogic device. Processors also include communication devices.

Additionally, the methods may be implemented by instructions beingperformed by a processor, and such instructions (and/or data valuesproduced by an implementation) may be stored on a computer readablestorage medium. A computer readable storage medium may take the form ofa computer readable program product embodied in one or more computerreadable medium(s) and having computer readable program code embodiedthereon that is executable by a computer. A computer readable storagemedium as used herein may be considered a non-transitory storage mediumgiven the inherent capability to store the information therein as wellas the inherent capability to provide retrieval of the informationtherefrom. A computer readable storage medium may be, for example, butis not limited to, an electronic, magnetic, optical, electromagnetic,infrared, or semiconductor system, apparatus, or device, or any suitablecombination of the foregoing. It is to be appreciated that thefollowing, while providing more specific examples of computer readablestorage mediums to which the present embodiments may be applied, ismerely an illustrative and not an exhaustive listing as is readilyappreciated by one of ordinary skill in the art: a portable computerdiskette; a hard disk; a read-only memory (ROM); an erasableprogrammable read-only memory (EPROM or Flash memory); a portablecompact disc read-only memory (CD-ROM); an optical storage device; amagnetic storage device; or any suitable combination of the foregoing.

The instructions may form an application program tangibly embodied on aprocessor-readable medium.

Instructions may be, for example, in hardware, firmware, software, or acombination. Instructions may be found in, for example, an operatingsystem, a separate application, or a combination of the two. A processormay be characterized, therefore, as, for example, both a deviceconfigured to carry out a process and a device that includes aprocessor-readable medium (such as a storage device) having instructionsfor carrying out a process. Further, a processor-readable medium maystore, in addition to or in lieu of instructions, data values producedby an implementation.

An apparatus may be implemented in, for example, appropriate hardware,software, and firmware. Examples of such apparatus include personalcomputers, laptops, smartphones, tablet computers, digital multimediaset top boxes, digital television receivers, personal video recordingsystems, connected home appliances, head mounted display devices (HMD,see-through glasses), projectors (beamers), “caves” (system includingmultiple displays), servers, video encoders, video decoders,post-processors processing output from a video decoder, pre-processorsproviding input to a video encoder, web servers, set-top boxes, and anyother device for processing a point cloud, a video or an image or othercommunication devices. As should be clear, the equipment may be mobileand even installed in a mobile vehicle.

Computer software may be implemented by the processor 6010 or byhardware, or by a combination of hardware and software. As anon-limiting example, the embodiments may be also implemented by one ormore integrated circuits. The memory 6020 may be of any type appropriateto the technical environment and may be implemented using anyappropriate data storage technology, such as optical memory devices,magnetic memory devices, semiconductor-based memory devices, fixedmemory, and removable memory, as non-limiting examples. The processor6010 may be of any type appropriate to the technical environment, andmay encompass one or more of microprocessors, general purpose computers,special purpose computers, and processors based on a multi-corearchitecture, as non-limiting examples.

As will be evident to one of ordinary skill in the art, implementationsmay produce a variety of signals formatted to carry information that maybe, for example, stored or transmitted. The information may include, forexample, instructions for performing a method, or data produced by oneof the described implementations. For example, a signal may be formattedto carry the bitstream of a described embodiment. Such a signal may beformatted, for example, as an electromagnetic wave (for example, using aradio frequency portion of spectrum) or as a baseband signal. Theformatting may include, for example, encoding a data stream andmodulating a carrier with the encoded data stream. The information thatthe signal carries may be, for example, analog or digital information.The signal may be transmitted over a variety of different wired orwireless links, as is known. The signal may be stored on aprocessor-readable medium.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used herein, thesingular forms “a”, “an”, and “the” may be intended to include theplural forms as well, unless the context clearly indicates otherwise. Itwill be further understood that the terms “includes/comprises” and/or“including/comprising” when used in this specification, may specify thepresence of stated, for example, features, integers, steps, operations,elements, and/or components but do not preclude the presence or additionof one or more other features, integers, steps, operations, elements,components, and/or groups thereof. Moreover, when an element is referredto as being “responsive” or “connected” to another element, it may bedirectly responsive or connected to the other element, or interveningelements may be present. In contrast, when an element is referred to asbeing “directly responsive” or “directly connected” to other element,there are no intervening elements present.

It is to be appreciated that the use of any of the symbol/term “/”,“and/or”, and “at least one of”, for example, in the cases of “A/B”, “Aand/or B” and “at least one of A and B”, may be intended to encompassthe selection of the first listed option (A) only, or the selection ofthe second listed option (B) only, or the selection of both options (Aand B). As a further example, in the cases of “A, B, and/or C” and “atleast one of A, B, and C”, such phrasing is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of the third listedoption (C) only, or the selection of the first and the second listedoptions (A and B) only, or the selection of the first and third listedoptions (A and C) only, or the selection of the second and third listedoptions (B and C) only, or the selection of all three options (A and Band C). This may be extended, as is clear to one of ordinary skill inthis and related arts, for as many items as are listed.

Various numeric values may be used in the present application. Thespecific values may be for example purposes and the aspects describedare not limited to these specific values.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements are notlimited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement without departing from the teachings of this application. Noordering is implied between a first element and a second element.

Reference to “one embodiment” or “an embodiment” or “one implementation”or “an implementation”, as well as other variations thereof, isfrequently used to convey that a particular feature, structure,characteristic, and so forth (described in connection with theembodiment/implementation) is included in at least oneembodiment/implementation. Thus, the appearances of the phrase “in oneembodiment” or “in an embodiment” or “in one implementation” or “in animplementation”, as well any other variations, appearing in variousplaces throughout this application are not necessarily all referring tothe same embodiment.

Similarly, reference herein to “in accordance with anembodiment/example/implementation” or “in anembodiment/example/implementation”, as well as other variations thereof,is frequently used to convey that a particular feature, structure, orcharacteristic (described in connection with theembodiment/example/implementation) may be included in at least oneembodiment/example/implementation. Thus, the appearances of theexpression “in accordance with an embodiment/example/implementation” or“in an embodiment/example/implementation” in various places in thespecification are not necessarily all referring to the sameembodiment/example/implementation, nor are separate or alternativeembodiment/examples/implementation necessarily mutually exclusive ofother embodiments/examples/implementation.

Reference numerals appearing in the claims are by way of illustrationonly and shall have no limiting effect on the scope of the claims.Although not explicitly described, the present embodiments/examples andvariants may be employed in any combination or sub-combination.

When a figure. is presented as a flow diagram, it should be understoodthat it also provides a block diagram of a corresponding apparatus.Similarly, when a figure is presented as a block diagram, it should beunderstood that it also provides a flow diagram of a correspondingmethod/process.

Although some of the diagrams include arrows on communication paths toshow a primary direction of communication, it is to be understood thatcommunication may occur in the opposite direction to the depictedarrows.

Various implementations involve decoding. “Decoding”, as used in thisapplication, may encompass all or part of the processes performed, forexample, on a received point cloud frame (including possibly a receivedbitstream which encodes one or more point cloud frames) in order toproduce a final output suitable for display or for further processing inthe reconstructed point cloud domain. In various embodiments, suchprocesses include one or more of the processes typically performed by animage-based decoder.

As further examples, in one embodiment “decoding” may refer only toentropy decoding, in another embodiment “decoding” may refer only todifferential decoding, and in another embodiment “decoding” may refer toa combination of entropy decoding and differential decoding. Whether thephrase “decoding process” may be intended to refer specifically to asubset of operations or generally to the broader decoding process willbe clear based on the context of the specific descriptions and isbelieved to be well understood by those skilled in the art.

Various implementations involve encoding. In an analogous way to theabove discussion about “decoding”, “encoding” as used in thisapplication may encompass all or part of the processes performed, forexample, on an input point cloud frame in order to produce an encodedbitstream. In various embodiments, such processes include one or more ofthe processes typically performed by an image-based decoder.

As further examples, in one embodiment “encoding” may refer only toentropy encoding, in another embodiment “encoding” may refer only todifferential encoding, and in another embodiment “encoding” may refer toa combination of differential encoding and entropy encoding. Whether thephrase “encoding process” may be intended to refer specifically to asubset of operations or generally to the broader encoding process willbe clear based on the context of the specific descriptions and isbelieved to be well understood by those skilled in the art.

Note that the syntax elements as used herein, for example, the flagoint_local_reconstruction_mode_present_flag is a descriptive term. Assuch, they do not preclude the use of other syntax element names.

Various embodiments refer to rate distortion optimization. Inparticular, during the encoding process, the balance or trade-offbetween the rate and distortion is usually considered, often given theconstraints of computational complexity. The rate distortionoptimization may be usually formulated as minimizing a rate distortionfunction, which is a weighted sum of the rate and of the distortion.There are different approaches to solve the rate distortion optimizationproblem. For example, the approaches may be based on an extensivetesting of all encoding options, including all considered modes orcoding parameters values, with a complete evaluation of their codingcost and related distortion of the reconstructed signal after coding anddecoding. Faster approaches may also be used, to save encodingcomplexity, in particular with computation of an approximated distortionbased on the prediction or the prediction residual signal, not thereconstructed one. A mix of these two approaches may also be used, suchas by using an approximated distortion for only some of the possibleencoding options, and a complete distortion for other encoding options.Other approaches only evaluate a subset of the possible encodingoptions. More generally, many approaches employ any of a variety oftechniques to perform the optimization, but the optimization is notnecessarily a complete evaluation of both the coding cost and relateddistortion.

Additionally, this application may refer to “determining” various piecesof information. Determining the information may include one or more of,for example, estimating the information, calculating the information,predicting the information, or retrieving the information from memory.

Further, this application may refer to “accessing” various pieces ofinformation. Accessing the information may include one or more of, forexample, receiving the information, retrieving the information (forexample, from memory), storing the information, moving the information,copying the information, calculating the information, determining theinformation, predicting the information, or estimating the information.

Additionally, this application may refer to “receiving” various piecesof information. Receiving is, as with “accessing”, intended to be abroad term. Receiving the information may include one or more of, forexample, accessing the information, or retrieving the information (forexample, from memory). Further, “receiving” is typically involved, inone way or another, during operations such as, for example, storing theinformation, processing the information, transmitting the information,moving the information, copying the information, erasing theinformation, calculating the information, determining the information,predicting the information, or estimating the information.

Also, as used herein, the word “signal” refers to, among other things,indicating something to a corresponding decoder. For example, in certainembodiments the encoder signals a particular syntax element SE and/orPLR metadata. In this way, in an embodiment the same parameter (PLRmetadata) may be used at both the encoder side and the decoder side.Thus, for example, an encoder may transmit (explicit signaling) aparticular parameter to the decoder so that the decoder may use the sameparticular parameter. Conversely, if the decoder already has theparticular parameter as well as others, then signaling may be usedwithout transmitting (implicit signaling) to simply allow the decoder toknow and select the particular parameter. By avoiding transmission ofany actual functions, a bit savings is realized in various embodiments.It is to be appreciated that signaling may be accomplished in a varietyof ways. For example, one or more syntax elements, flags, and so forthare used to signal information to a corresponding decoder in variousembodiments. While the preceding relates to the verb form of the word“signal”, the word “signal” may also be used herein as a noun.

A number of implementations have been described. Nevertheless, it willbe understood that various modifications may be made. For example,elements of different implementations may be combined, supplemented,modified, or removed to produce other implementations. Additionally, oneof ordinary skill will understand that other structures and processesmay be substituted for those disclosed and the resulting implementationswill perform at least substantially the same function(s), in at leastsubstantially the same way(s), to achieve at least substantially thesame result(s) as the implementations disclosed. Accordingly, these andother implementations are contemplated by this application.

1. A method comprising: signaling in a bitstream a first syntax elementrepresenting a Point Local Reconstruction mode, said Point LocalReconstruction mode being representative of at least one parameterdefining a mode for reconstructing at least one point of a point cloudframe, signaling a second syntax element per patch indicating whether asingle first syntax element is signaled once for all blocks of the patchor whether a first syntax element is signaled for each block of thepatch.
 2. The method of claim 1, wherein said Point Local Reconstructionmode is an index value of an entry of a look-up-table defining relationsbetween said index value and said at least one parameter relative tosaid mode.
 3. (canceled)
 4. The method of claim 1, wherein a patch beinga set of at least one block of at least one 2D sample representing anorthogonal projection of at least one 3D sample of a point cloud frameonto a projection plane.
 5. The method of claim 1, wherein signalingsaid second syntax element is responsive to a determination that a patchcontains more than a given number of blocks.
 6. The method of claim 1,wherein the method further comprises signaling a third syntax elementrepresenting a default mode. 7-18. (canceled)
 19. A method comprising:obtaining from a bitstream a first syntax element representing a PointLocal Reconstruction mode, said Point Local Reconstruction mode beingrepresentative of at least one parameter defining a mode forreconstructing at least one point of a point cloud frame, obtaining asecond syntax element per patch indicating whether a single first syntaxelement is obtained once for all blocks of a patch or whether a firstsyntax element is obtained for each block of a patch.
 20. The method ofclaim 19, wherein said information is an index value of an entry of alook-up-table defining relations between said index value and at leastone parameter relative to said mode.
 21. (canceled)
 22. The method ofclaim 19, wherein a patch being a set of at least one block of at leastone 2D sample representing an orthogonal projection of at least one 3Dsample of a point cloud frame onto a projection plane.
 23. The method ofclaim 19, wherein obtaining said second syntax element is responsive toa determination that a patch contains more than a given number ofblocks. 24-27. (canceled)
 29. An apparatus comprising one or moreprocessors configured to: signaling in a bitstream a first syntaxelement representing a Point Local Reconstruction mode, said Point LocalReconstruction mode being representative of at least one parameterdefining a mode for reconstructing at least one point of a point cloudframe, signaling a second syntax element per patch indicating whether asingle first syntax element is signaled once for all blocks of the patchor whether a first syntax element is signaled for each block of thepatch.
 30. The apparatus of claim 29, wherein said information is anindex value of an entry of a look-up-table defining relations betweensaid index value and at least one parameter relative to said mode. 31.(canceled)
 32. The apparatus of claim 29, wherein a patch being a set ofat least one block of at least one 2D sample representing an orthogonalprojection of at least one 3D sample of a point cloud frame onto aprojection plane.
 33. The apparatus of claim 7, wherein signaling saidsecond syntax element is responsive to a determination that a patchcontains more than a given number of blocks. 34-46. (canceled)
 47. Anapparatus comprising one or more processors configured to obtaining froma bitstream a first syntax element representing a Point LocalReconstruction mode, said Point Local Reconstruction mode beingrepresentative of at least one parameter defining a mode forreconstructing at least one point of a point cloud frame, obtaining asecond syntax element per patch indicating whether a single first syntaxelement is obtained once for all blocks of a patch or whether a firstsyntax element is obtained for each block of a patch.
 48. The apparatusof claim 47, wherein said information is an index value of an entry of alook-up-table defining relations between said index value and at leastone parameter relative to said mode.
 49. (canceled)
 50. The apparatus ofclaim 47, wherein a patch being a set of at least one block of at leastone 2D sample representing an orthogonal projection of at least one 3Dsample of a point cloud frame onto a projection plane.
 51. The apparatusof claim 47, wherein obtaining said second syntax element is responsiveto a determination that a patch contains more than a given number ofblocks.
 52. The apparatus of claim 47, wherein said one or moreprocessors are further configured to obtaining a third syntax elementrepresenting a default mode. 53-55. (canceled)
 56. A non-transitorycomputer-readable medium including a bitstream comprising: a firstsyntax element representing a Point Local Reconstruction mode, saidPoint Local Reconstruction mode being representative of at least oneparameter defining a mode for reconstructing at least one point of apoint cloud frame, a second syntax element per patch indicating whethera single first syntax element is obtained once for all blocks of a patchor whether a first syntax element is obtained for each block of a patch.57. (canceled)
 58. A non-transitory computer-readable medium includinginstructions for causing one or more processors to carry out a methodaccording to claim
 1. 59-60. (canceled)